Use of multiple optical channels, such as optical fibers, has become prevalent in applications ranging from data communications to optical computing in response to a need for increased system bandwidth. At the same time, miniaturization still remains an important goal in these applications. High fiber packing density assists in effecting miniaturization and increasing the space-bandwidth product. In addition, precise positioning of the fiber core is a critical goal in achieving acceptable system performance, since the fiber core must be precisely registrable to other devices or fibers of the system. A fiber array provides a desirable way for handling multiple optical fibers while attempting to effect miniaturization and providing precision registration among the fibers.
Typically, a fiber includes an inner core and cladding enclosed within a buffer and an outer jacketing. For maximizing packing density, only the information carrying portions of the fiber, core and surrounding cladding, need be accessible at the input and output portions of an array. The buffer and jacketing, which typically surround the cladding, provide structural support for the core and cladding but perform no optical function. For example, a fiber may have a jacketing diameter of 250 microns and cladding diameter of 125 microns. Therefore, removal of the jacketing and any intermediate buffer permits an increase in the linear packing density by a factor of 2.
In addition to the desirability of providing high packing density, providing precise and stable positioning of one fiber core relative to another is critical to optical performance. Without precise relative positioning among the signal-carrying portions of fibers, i.e., the fiber core, unacceptably large variation or degradation in optical performance, such as coupling and insertion losses, may result. Movement or misalignment between fiber cores on the sub-micron scale may give rise to such unacceptable performance. For example, a core diameter of 8 microns is a typical dimension in single-mode fibers having the above-listed jacketing and cladding diameters. Thus, movement or misalignment of the optical core by even 1 micron represents movement or misalignment by a substantial fraction of the core diameter.
In addition, in many applications it becomes highly desirable to provide such sub-micron precision over a product lifetime of 20 years or more. In order to maximize product lifetime for structures that include optical fibers secured to a support element and to each other, the materials and fabrication methods used in the fabrication of fiber arrays must be environmentally stable in order to durably attach the optical fibers to the support element over a period of decades.
One factor in effecting fiber array stability is the choice of bonding material utilized to secure the fibers to the support element. Bonding materials presently used can suffer from a number of deficiencies. For example, presently used bonding materials typically possess a coefficient of thermal expansion unacceptably different from those of the optical fiber and support element to which the fiber is secured. The difference in thermal expansion coefficient may affect the stability and relative position of the fibers when exposed to temperature changes. In addition, some commonly used bonding materials may absorb moisture which can significantly reduces the ability of the bonding material to firmly secure the optical fibers to each other and to the support element. The absorption of moisture may also tend to swell the bonding material, which can cause dimensional changes to the bonding material that strain the attachment between the optical fibers and the support element. For example, movement or even detachment of the optical fibers from the support element may result from the dimensional changes of the bonding material. Furthermore, prolonged exposure to other environmental conditions, such as thermal, oxidative and photo degradation may cause a breakdown of the bonding material over such periods of exposure. Another disadvantage associated with the use of certain bonding materials is the requirement for unacceptably lengthy cure schedules, often at elevated temperatures, which can substantially hinder high volume production.
Hence there remains a need in the art for materials and methods for providing fiber arrays having fiber cores that are precisely positioned and reliably secured relative to one another and to a support element.